National Party candidate Mark Osborne is far behind in the polls with two days until Saturday's by-election.

Mr Key said he had always intended to return to the electorate to show Northlanders that the National Party cared about them and wanted to retain the seat.

He said his immediate appearance there, direct from Japan, was not a sign that National was desperate.

"No, the counter-argument would be that I was off-shore doing something, it was great work for New Zealand but I didn't care about the people of Northland. We're in a by-election, we're fighting hard for that."

He talked down the significance of Wednesday's 3News-Reid Research poll, which put New Zealand First leader Winston Peters ahead of Mr Osborne by 20 points, saying it was no indication of National losing voter support more widely.

It surveyed 501 Northland voters and has a margin of error of plus or minus 4 percent.

"By-elections can be very quirky things, I mean, for a start-off, our national polling is very high and it remains high." Mr Key said, adding that National was fighting hard for the seat.

"We're in a by-election and we know we are up against it. You've got all the other political parties coalescing around Winston Peters but we've got a great candidate and lot of National voters."

However, leading Northland farmer Richard Drake said Mr Osborne has been done no favours by having senior politicians continually babysit him.

Mr Drake was among Dargaville community leaders at a meeting yesterday with Deputy Prime Minister Bill English, and Mr Osborne - who didn't speak.

"People who meet him one to one can see that he's got potential, he's got a broad range of knowledge and understanding of the issues. In some ways I think he's been frustrated by his own party in a bit of an overkill."

Turns out the guy who's transformed Osborne's hoarding into Peters' one is a candidate: Bruce Rogan from Mangawhai. pic.twitter.com/TWSlCDvqFP